Conventionally, in the field of manufacture of a semiconductor device, a low-k film such as a SiCHO-based film has been used as an insulating layer, e.g., an interlayer insulating film. It has been considered to further reduce a dielectric constant of such a SiCHO-based low-k film by forming pores in the low-k film, i.e., forming a porous low-k film and increasing the porosity thereof.
If a trench or a hole is formed in such a porous low-k film by plasma etching or the like, an inner wall of the trench or the hole exposed to plasma may be damaged and deteriorated. As a solution, there has been known a method of recovering damage by providing a recovery agent containing hydrocarbon to the trench or the hole (see, for example, Patent Document 1).
Further, if the trench or the hole is formed in the porous low-k film as mentioned above, the pores may be exposed on an inner wall of the trench or the hole. Thus, roughness of the inner wall of the trench or the hole may be increased, which in turn causes an increase of resistance of a barrier metal or a copper wiring buried in the trench or the hole. Furthermore, if the pores are not separated but connected as a continuous hole, a wiring metal may be diffused even to the inside of the low-k film through the continuous hole, resulting in electrical leakage. To solve the problem, there has been known a method of forming a sealing layer on an exposed portion of the low-k film by CVD or the like (see, for example, Patent Document 2).    Patent Document 1: Japanese Patent Laid-open Publication No. 2006-210774    Patent Document 2: Japanese Patent Laid-open Publication No. 2008-509543
As stated above, if the porous low-k film is used in the semiconductor device, the pores may be exposed on an inner sidewall of the trench or the hole when the trench or the hole for burying therein the wiring metal is formed in the low-k film. As a result, the metal may diffuse within the pores, raising a likelihood of generation of electrical leakage. Further, roughness of the inner sidewall may be increased, resulting in increase of wiring resistance as well. These problems may become remarkable when the dielectric constant of the low-k film is further reduced by increasing the porosity of the low-k film.
Moreover, when the method of forming the sealing layer by the CVD or the like is used to avoid these problems, a sealing layer may also be formed on an underlying copper wiring exposed on a bottom of the trench or the hole. Thus, a sealing layer removing process for removing this sealing layer on the copper wiring needs to be performed, which may result in deterioration of productivity due to increase of the number of required processes.